1. Technical Field
This invention relates to crank shaft bearings of the type having side flanges for accommodating high thrust loads.
2. Related Art
It is common practice to support internal combustion engine crank shafts with journal bearings located at spaced points along the crank shaft. At least one of the bearings is designed to support axial thrust forces applied through the crank shaft. Such thrust bearings are made in bearing halves, each half bearing including a semi-cylindrical bearing shell having a concave inner running surface and a pair of axially spaced flanges projecting radially outwardly of the shell and having axially outwardly facing thrust bearing surfaces. The thrust surfaces seat against associated side surfaces of the crank shaft arms, such that the shaft is prevented from shifting in the axial direction during operation.
In some applications, there is considerable axial loading and measures must be taken to protect the thrust surfaces of the bearing. U.S. Pat. No. 5,192,136 discloses such a bearing, wherein the thrust face is formed with a plurality of oil supply grooves that subdivide the thrust bearing surface into a plurality of thrust pads. Each thrust pad is contoured to generate a protective hydrodynamic wedge film thrust support action, in order to separate the two opposing surfaces and to prevent metal-to-metal contact between the thrust face and under axial loading. The thrust bearing surface profile shown generally in FIG. 5 is in use. Such a prior art bearing is also illustrated in FIG. 7 of the present application. It has been found that in some installations, thrust bearings of the above type tend to distort under heavy clamping load, as illustrated schematically in FIG. 8, and the degree of distortion is constantly changing with changes in operating temperature and axial load conditions on the bearing. Studies of the load profile across the prior thrust bearing surface are illustrated in FIG. 9 of the present application. The profile shows that high loading is carried at points along the thrust face including a location of an extremely high pressure peak at the trailing end of the half bearing in relation to the direction of rotation of the crank shaft across the bearing surface. Over time, the heavy loading and cyclic distortion changes that occur can fatigue the trailing end of the thrust face where the flange meets the bearing shell. In severe cases, such fatigue can lead to delamination of the bearing layer material and/or cracking of the thrust flange at the trailing end where it meets the bearing shell.
It is an object of the present invention to overcome the shortcomings of prior hydrodynamic thrust bearings.
A half bearing for a rotary shaft includes a bearing shell having a concave running surface. At least one thrust flange extends radially from the shell and has an axially facing thrust bearing surface extending circumferentially in a sliding direction of the thrust bearing surface corresponding to the direction of rotation of the rotary shaft. The thrust bearing surface has a leading end and a trailing end relative to the sliding direction of the bearing surface. The thrust bearing surface includes a plurality of circumferentially spaced oil supply grooves which extend radially of the thrust bearing surface and subdivide the surface into a plurality of thrust bearing pads. The thrust bearing pads includes a leading pad disposed between the leading end and leading oil supply groove. The thrust pads include a trailing pad disposed between the trailing end and groove of the thrust bearing surface. Each thrust bearing pad has a hydrodynamic contour which includes an inclined ramp surface extending in the sliding direction, and a raised land surface following the inclined ramp surface in the sliding direction. According to the invention, the spacing between the trailing groove and trailing end is greater than the distance between the leading groove and leading end. The land surface of the trailing thrust bearing pad is spaced from the trailing end of the thrust bearing surface by distance greater than a distance between the land surface of the leading thrust bearing pad and the leading groove.
This construction of the thrust face according to the invention has the advantage of controlling the distribution of the hydrodynamic load imparted by the rotating crankshaft on the bearing. More specifically, spacing the land surface of the trailing thrust pad further from the trailing end has the advantage of shifting the peak high pressure location, which occurs at the land, away from the trailing end of the thrust flange, thereby isolating the otherwise problematic corner region of the trailing end which is prone to fatigue failure as described in the previous section. In other words, adjusting the relative location of the oil supply grooves and high pressure land regions enables a corresponding shifting of the peak pressure location away from the trailing end of the thrust bearing, overcoming the fatigue and delamination failure problems associated with the prior bearings discusses in the previous section. The oil groove design also enables adequate oil supply and better hydrodynamic film generation.
The invention has the further advantage of utilizing standard manufacturing techniques, coupled with controlled modification of the process, to yield a more reliable, high performance thrust bearing. Tests conducted on flange bearings constructed according to the present invention reveal that the subject thrust bearings are able to sustain a significantly higher average maximum load in use under severe testing conditions without experiencing high levels of localized torque, wear or fatigue failure associated with the prior hydrodynamic thrust bearing constructions operating under the same or comparable conditions.